The ornamental design for a lightingfixture, as shown and described.
The single FIGURE is a left perspective view of a lighting fixture showing the new design, for which a right perspective view of the lighting fixture would be a mirror image thereof.
The broken lines form no part of the claimed design and either represent the bounds of the claimed design (e.g., the broken lines immediately adjacent shaded areas and the broken lines immediately adjacent portions of the design represented in solid lines) or are directed to environment (e.g., different portions of the shades) and are for illustrative purposes only.